The present invention relates to a service interruption minimizing system for a power distribution line and an operational method therefor, and more particularly, it relates to a service interruption minimizing system for a power distribution line which ensures a continuous operation of the distribution line in the case of a restorative fault which may occur on the distribution line, and the operational method therefor.
Conventional operation to remove a fault section on the distribution line is based on a time sequential protective method. One such example is set forth in the "Distribution Line Technical Manual" pp 464-465 issued from Ohm KK., Nov. 30, 1991.
In brief, according to this prior art method, a protective relay installed in a substation is operated when a fault occurs to interrupt a circuit breaker connected to the distribution line and switchgears disposed along the distribution line, are opened due to the out-of-voltage on the distribution line. Then, a restoration operation for restoring the power outage section starts with a reclosing of the circuit breaker. More specifically, the restoration proceeds as follows: a first switchgear located on the distribution line closest to the circuit breaker is reclosed by being applied with a voltage upon reclosing of the circuit breaker, then another switchgear next to the first switch is reclosed by being applied with a voltage upon reclosing of the first switch, to be followed sequentially by the subsequent switchgears. When a fault which occurs on the distribution line is a restorative one and the fault can be removed by opening the circuit breaker, a subsequent restoration operation can be carried out to settle the power outage. Further, if a fault is a persistent-cause fault, the circuit breaker is opened once again, permitting power supply only on the power side section of the fault section, thereby causing the subsequent sections of the distribution line to be cut off from the power supply.
The outline of the prior art time sequential protective method is as described above. This, however, has such a problem that there occurs an outage of power lasting about 30 to 60 seconds due to the opening of the circuit breaker. The recent wide applications and proliferation of computer systems have been such that any power outage itself is no more tolerated to occur in the distribution lines. Therefore, it is desired to realize a service interruption minimizing system suitable for the distribution lines, which is capable of supplying an uninterrupting power supply as much as possible, and a method thereof.
Incidentally, the faults occurring on the distribution lines, which is can be classified roughly into short-circuits and ground faults, with their ratios of occurrence being 2 and 8 accordingly. Moreover, 80 to 90 percent of the ground faults of the distribution lines are restorative-cause faults which occur due to mere contacting of branches of trees or the like.
According to the conventional time sequential protection method, even if a ground fault may be such a restorative-cause one as above, a preset protection sequence of the aforementioned steps is allowed to proceed, eventually causing a power outage.